	// 1+....+n

	import java.io.*;

public class HW7_1SP1 {


	   public static void main(String args[]) throws IOException
	   {
	      int n, sum;
	      BufferedReader buf;
	      String str;
	      
	      buf=new BufferedReader(new InputStreamReader(System.in));
	      
	      while(true){
	      
	         str=input(buf);
	         if(str.equals("stop"))
	            break;
	            
	         if(!whetherInt(str))
	         {
	            System.out.println("input is wrong. input again!");
	            continue;
	         }
	      
	         n=Integer.parseInt(str);
	      
	         sum=addTo(n);
	         System.out.println("\n1+....+n="+sum);
	      }
	      
	   }
	      
	   
	   public static Boolean whetherInt(String str)
	   {
	      char[] charS;
	      
	      charS=str.toCharArray();
	      for(int i=0; i<charS.length;i++)
	         if(charS[i]<'0'||charS[i]>'9')
	            return false;
	            
	                     
	      return true;   
	               
	   }
	   
	   public static String input(BufferedReader buf) throws IOException
	   {
	      String str;
	      
	      System.out.print("Please input the number n:");
	      str=buf.readLine();
	      
	      return str;
	   }
	   
	   private static int addTo(int n)
	   {
	      int sum=0;
	      for(int i=1;i<=n;i++)
	         sum+=i;
	      
	      return sum;
	   }
	}

